Tandem axles are used in heavy load carrying vehicles such as trucks and busses. Tandem axles provide a means for transferring torque from the engine drive shaft to successive or tandem axles on the truck. Additionally, tandem axles distribute heavy loads over multiple axles to avoid excessive loads on a single axle. Tandem axles further provide improved traction for adverse road conditions. Inter axle differential mechanisms divide power from a single drive shaft to two separate axle assemblies. One such tandem axle assembly having an inter axle differential is disclosed in U.S. Pat. No. 4,754,847 (Glaze et al.). Another tandem axle assembly is disclosed in U.S. Pat. No. 4,050,534 (Nelson et al.). Typical tandem axle assemblies are not particularly fuel efficient.
U.S. Pat. No. 4,271,722 (Campbell) describes a differential for a four-wheel drive vehicle that includes an integral remotely operable disconnect. Conventional disconnect assemblies do not have overdrive systems and are also not particularly fuel efficient.
U.S. Pat. No. 5,711,389 (Schlosser) describes a tandem rear drive axle assembly that is capable of selectively driving either one or both axles without the use of an inter axle differential. The drive axle assembly includes an input shaft connected to a first axle. A clutch pack is used to selectively engage and disengage a second axle. A clutch actuator assembly is used to automatically actuate the clutch when driving of the second axle is desired.